The optimal thermo-optical properties and energy saving potential of adaptive glazing technologies

The development of dynamic building envelope technologies, which adapt to changing outdoor and indoor environments, is considered a crucial step towards the achievement of the nearly Zero Energy Building target. It is currently not possible to evaluate the energy saving potential of innovative adaptive transparent building envelopes in an accurate manner. This creates difficulties in selecting between competing technologies and is a barrier to systematic development of these innovative technologies. The main aim of this work is to develop a method for devising optimal adaptive glazing properties and to evaluate the energy saving potential resulting from the adoption of such a technology. The method makes use of an inverse performance-oriented approach, to minimize the total primary energy use of a building. It is applied to multiple case studies (office reference room with 4 different cardinal orientations and in three different temperate climates) in order to evaluate and optimise the performance of adaptive glazing as it responds to changing boundary conditions on a monthly and daily basis. A frequency analysis on the set of optimised adaptive properties is subsequently performed to identify salient features of ideal adaptive glazing. The results show that high energy savings are achievable by adapting the transparent part of the building envelope alone, the largest component being the cooling energy demand. As expected, the energy savings are highly sensitive to: the time scale of the adaptive mechanisms; the capability of the façade to adapt to the outdoor climatic condition; the difference between outdoor climatic condition and the comfort range. Moreover important features of the optimal thermo-optical properties are identified. Of these, one of the most important findings is that a unique optimised technology, varying its thermo-optical properties between a limited number of states could be effective in different climates and orientations.The present work has been developed in the framework of a PhD research project. The authors are grateful to EPSRC and Wintech Ltd. for funding the PhD. The authors are also grateful to the National Natural Science Foundation of China (No. 51408427) for their support.This is the final published version of the article. It was originally published in Applied Energy (Favoino F, Overend M, Jin Q, Applied Energy, 2015, 156, 1-15, doi:10.1016/j.apenergy.2015.05.065). The final version is available at http://dx.doi.org/10.1016/j.apenergy.2015.05.06

Thermo-chromic glazing in buildings: a novel methodological framework for a multi-objective performance evaluation

Abstract Transparent adaptive facade components can improve the energy performance and the indoor environmental quality of buildings. Nevertheless, their utilization is not widespread, due also to the lack of a robust methodology to comprehensively evaluate their potentialities and find out their most suitable applications. The present paper introduces a novel methodology to characterize the behavior of a transparent adaptive facade component, a thermo-chromic glazing, and predict its effects, through numerical simulations, on energy performance and visual comfort aspects. An experimental characterization on the thermo-chromic glazing was performed to determine its optical properties at the variation of its surface temperature. The component was found to be able to switch its visible transmittance between 0.71 and 0.13, and its solar transmittance between 0.65 and 0.28. The experimental results were used to feed the numerical model created on purpose to describe the adaptive behavior of the component. Finally, a numerical simulation campaign was performed to assess the effects of the thermo-chromic glazing on energy and visual comfort aspects of an enclosed office located in Turin. It was found that the thermo-chromic glazing reduced the overall energy performance compared to a static selective glazing, but it allows improving the visual comfort conditions within the space considered

Optimal control and performance of photovoltachromic switchable glazing for building integration in temperate climates

The development of adaptive building envelope technologies, and particularly of switchable glazing, can make significant contributions to decarbonisation targets. It is therefore essential to quantify their effect on building energy use and indoor environmental quality when integrated into buildings. The evaluation of their performance presents new challenges when compared to conventional “static” building envelope systems, as they require design and control aspects to be evaluated together, which are also mutually interrelated across thermal and visual physical domains. This paper addresses these challenges by presenting a novel simulation framework for the performance evaluation of responsive building envelope technologies and, particularly, of switchable glazing. This is achieved by integrating a building energy simulation tool and a lighting simulation one, in a control optimisation framework to simulate advanced control of adaptive building envelopes. The performance of a photovoltachromic glazing is evaluated according to building energy use, Useful Daylight Illuminance, glare risk and load profile matching indicators for a sun oriented office building in different temperate climates. The original architecture of photovoltachromic cell provides an automatic control of its transparency as a function of incoming solar irradiance. However, to fully explore the building integration potential of photovoltachromic technology, different control strategies are evaluated, from passive and simple rule based controls, to optimised rule based and predictive controls. The results show that the control strategy has a significant impact on the performance of the photovoltachromic switchable glazing, and of switchable glazing technologies in general. More specifically, simpler control strategies are generally unable to optimise contrasting requirements, while more advanced ones can increase energy saving potential without compromising visual comfort. In cooling dominated scenarios reactive control can be as effective as predictive for a switchable glazing, differently than heating dominated scenarios where predictive control strategies yield higher energy saving potential. Introducing glare as a control parameter can significantly decrease the energy efficiency of some control strategies, especially in heating dominated climates.This work was conducted as part of a PhD research sponsored by UK EPSRC and Wintech Ltd. The authors acknowledge the support of the COST Action TU1403 – Adaptive Facades Network (www.adaptivefacade.eu) and the University of Sydney (IPDF fund). The experimental data used as an input in this work were partially supported by Regione PUGLIA (APQ Reti di Laboratorio, project “PHOEBUS” cod. 31) and by Italian Minister for Education and Research which funded the R&D program “MAAT” (PON02_00563_3316357 − CUP B31C12001230005). The devices were fabricated at the Center for Biomolecular Nanotechnologies of Istituto Italiano di Tecnologia and characterized in the laboratories of CNR-Nano in Lecce. The contribution of the fourth author to the work reported in this paper was supported by the Australian Research Council through its Future Fellowship scheme (FT140100130).This is the final version of the article. It first appeared from Elsevier at http://dx.doi.org/10.1016/j.apenergy.2016.06.107

Tracer gas techniques for airflow characterization in double skin facades

Monitoring airflow rates and fluid dynamics phenomena in the ventilated cavity is a challenging aspect of the experimental assessment of the performance of double-skin facades (DSF). There are various methods to characterize the fluid-dynamics behavior of DSF, but each of these has its advantages and drawbacks. This paper presents the airflow characterization in the cavity of a double-skin façade installed in a full-scale outdoor facility through various methods, and, more specifically, it compares two tracer gas methods with the velocity traverse method. In the paper, we highlight how different characterization results can be explained by considering the features of each method, and how these differences are linked to velocity ranges and airflows in the cavity. By discussing (i) the challenges of these methods and their applicability, (ii) the requirements in terms of experimental set-up and (iii) the limitations linked to instrumentation, we aim to enhance the discussion on experimental methods for advanced building envelope characterization and contribute to a more grounded understanding of the suitability of tracer gas methods for in-field characterization of airflows in facades

Building Performance Simulation and Characterisation of Adaptive Facades:

The book “Performance Simulation and Characterisation of Adaptive Facades” responds to the need of providing a general framework, standardised and recognised methods and tools to evaluate the performance of adaptive facades in a quantitative way, by means of numerical and experimental methods, in different domains of interest. This book represents the main outcome of the activities of the Working Group 2 of the COST Action TU1403 Adaptive Façades Network, “Components performance and characterisation methods”, by integrating in one publication the main deliverables of WG2 described in the Memorandum of Understanding: D 2.1. Report on current adaptive facades modelling techniques; D 2.4. Report on the validation of developed simulation tools and models; D 2.5. Report on the developed experimental procedures. These are extended by additional sections regarding structural aspects and key performance indicators for adaptive façade systems. This book is a comprehensive review of different areas of research on adaptive façade systems and provides both general and specific knowledge about numerical and experimental research methods in this field. The fast pace at which building technologies and materials develop, is slowly but constantly followed by the development of numerical and experimental methods and tools to quantify their performance. Therefore this book focuses primarily on general methods and requirements, in an attempt to provide a coherent picture of current and near future possibilities to simulate and characterise the performance of adaptive facades in different domains, which could remain relevant in the coming years. In addition, specific know-how on selected cases is also presented, as a way to clarify and apply the more general approaches and methods described. The present book is published to support practitioners, researchers and students who are interested in designing, researching, and integrating adaptive façade systems in buildings. It targets both the academic and the not-academic sectors, and intends to contribute positively to an increased market penetration of adaptive façade systems, components and materials, aimed at rationalising energy and material resources while achieving a high standard of indoor environmental quality, health and safety in the built environment

A novel methodology to spatially evaluate DGP classes by means of vertical illuminances. Preliminary results

A novel methodology to overcome the main limit of the Daylight Glare Probability DGP (i.e. the heavy computational time for an annual analysis of the DGP profile in one point) is presented. This uses a proxy based on the vertical illuminance (Ev) at the eye level. To do so, the most suitable value of Ev, to substitute DGP, is found by means of a comparison to the corresponding DGP value through a fault-detection diagnosis technique. The methodology was applied to a representative enclosed office with one South-facing window (Window-to-Wall Ratio of 50%) located in Turin. The glazing was assumed to have different transmission properties (specular and scattering) with different visible transmittances (in the range 3%-66%). The error in the estimation of the DGP classes calculated through the eye vertical illuminance was evaluated, for an analysis period of a whole year. The main advantages of the methodology proposed lie (i) in a significant reduction of the computational time required for its application and (ii) in the possibility of evaluating glare conditions not only for one or few points, but for a grid of points across a considered space. Its main limitation lies on its inability to quantify the exact DGP value, returning instead, at every time-step, the DGP class of performance

Thermo-mechanical Investigation of Novel GFRP-glass Sandwich Facade Components

Modern building envelopes are typically high-technological systems that need to meet strict requirements regarding architectural intent, structural capacity, energy-efficiency and durability. The study presented in this paper is based on recent research performed at the Glass & Façade Technology Research Group (University of Cambridge) that investigates high-performance engineered unitised systems as an alternative to traditional curtain-walls for building facades. The proposed unitised systems has a sandwich design made of two outer glass face sheets separated by, and bonded to, glass fibre-reinforced polymer (GFRP) pultruded profiles. This arrangement results in a lightweight and slim structure that could potentially provide high structural and thermal performances. Results discussed in this paper constitute a preliminary outcome of an extended investigation aimed to assess and compare, by means of Finite Element (FE) numerical simulations, the thermal and structural performances of novel frame-integrated (GFRP-glass) sandwich systems and traditional non-integrated frame curtain wall systems. The reported FE results, as shown, give evidence of the potential of the novel design concept, with improved thermal and structural performances compared to traditional non-integrated systems (up to +10% and +15%, respectively)

Simulating Switchable Glazing with EnergyPlus: An Empirical Validation and Calibration of a Thermotropic Glazing Model

Adaptive transparent building envelope technologies could play a significant role in decreasing energy use in buildings and providing a more comfortable indoor environment. In order to evaluate these potentials in an economic and accurate manner, it is essential to have numerical models and simulation tools which correctly reproduce the behaviour of such components at the building level. This paper presents and discusses the empirical validation of models for thermo-tropic glazing, a specific adaptive transparent glazing, by means of a whole building performance simulation tool, EnergyPlus. Moreover, this study highlights the differences between two modelling approaches (EnergyPlus built-in and EMS models) and experimental data. Negligible differences are noted between the two modelling approaches, even though the models do not completely agree with experimental data unless a model calibration is performed. The EMS modelling approach could be successfully extended to other dynamic glazing technologies that do not have a builtin model available in EnergyPlus, provided that an accurate thermo-optical characterisation of the dynamic glazing is available

Building Performance Simulation and Characterisation of Adaptive Facades

The book “Performance Simulation and Characterisation of Adaptive Facades” responds to the need of providing a general framework, standardised and recognised methods and tools to evaluate the performance of adaptive facades in a quantitative way, by means of numerical and experimental methods, in different domains of interest. This book represents the main outcome of the activities of the Working Group 2 of the COST Action TU1403 Adaptive Façades Network, “Components performance and characterisation methods”, by integrating in one publication the main deliverables of WG2 described in the Memorandum of Understanding: D 2.1. Report on current adaptive facades modelling techniques; D 2.4. Report on the validation of developed simulation tools and models; D 2.5. Report on the developed experimental procedures. These are extended by additional sections regarding structural aspects and key performance indicators for adaptive façade systems. This book is a comprehensive review of different areas of research on adaptive façade systems and provides both general and specific knowledge about numerical and experimental research methods in this field. The fast pace at which building technologies and materials develop, is slowly but constantly followed by the development of numerical and experimental methods and tools to quantify their performance. Therefore this book focuses primarily on general methods and requirements, in an attempt to provide a coherent picture of current and near future possibilities to simulate and characterise the performance of adaptive facades in different domains, which could remain relevant in the coming years. In addition, specific know-how on selected cases is also presented, as a way to clarify and apply the more general approaches and methods described. The present book is published to support practitioners, researchers and students who are interested in designing, researching, and integrating adaptive façade systems in buildings. It targets both the academic and the not-academic sectors, and intends to contribute positively to an increased market penetration of adaptive façade systems, components and materials, aimed at rationalising energy and material resources while achieving a high standard of indoor environmental quality, health and safety in the built environment